1. Field of the Invention
This invention relates to air-operated percussive action machines used in civil engineering and mining, and more particularly to machines, for driving holes in the ground.
2. Description of Related Art
There is known a reversible air-operated percussive action machine for driving holes in the ground (cf., e.g., USSR Inventor's Certificate No. 238,424; IPC E 02 F; F 06 e) comprising a housing, a hammer, an air distributor and an air feeding hose. The air distributor has the form of a tube connected to the air feeding hose. The outer surface of the tube is provided with a threaded portion to connect the tube to the housing. The tube has stop elements for limiting the axial travel thereof relative to the housing. The frontmost position of the tube ensures the forward percussive action of the machine, whereas the rearmost position of the tube corresponds to the reverse percussive action. The tube is moved from one extreme position to the other manually by turning the air feeding hose.
However, manual rotation of the hose when its length is greater than 40 m is a rather labour-consuming procedure. In addition, the above arrangement fails to assure reliable locking of the tube in the extreme positions, which may result in an unpredicted switchover in the percussive action mode of operation.
There is also known a reversible air-operated percussive action machine for driving holes in the ground (cf., USSR Inventor's Certificate No. 292,529; IPC E 02 F 5/18) comprising a housing, a hammer, an air distributor, and an air feeding hose. The air distributor is comprised of a sleeve fixedly secured relative to the housing, and a spring-loaded tube capable of movements relative to the sleeve.
The tube is provided with shaped lugs received by shaped grooves made in the sleeve. A switchover of the machine from the forward percussive action to the reverse and vice versa is done by terminating the supply of compressed air and repeated admission thereof to the air feeding hose. In the absence of air pressure the tube is acted upon by the spring to be moved axially and turned inside the sleeve at a certain angle. Readmission of compressed air results in that the tube is locked in a new position corresponding to a required successive percussive action of the machine.
Therefore the switchover in the percussive action mode is done after each successive termination of the supply of compressed air and readmission thereof to the machine. For example, if the machine operates in the forward percussive action mode, the successive operating mode will be the reverse percussive action of the machine.
One disadvantage of the aforedescribed machine resides in impossibility of arbitrary variations in the percussive action modes, which leads to certain inconveniencies in operation. In addition, because the preset percussive action mode prior to starting the machine by admitting compressed air thereto, the operator is prone to accidental injury.
There is further known a reversible percussive action machine for driving holes in the ground (cf., USSR Inventor's Certificate No. 652,279; IPC E 02 F 5/18) comprising a housing, an air distributor, and an air feeding hose. The air distributor includes a tube fixedly secured inside the housing, and a spring-loaded valving member built into the tube, the valving member being connected to the air feeding hose. The valving member has a lock means enabling to lock the valving member is two extreme positions providing for two percussive actions of the machine. The valving member is moved from the extreme front position corresponding to the forward percussive action of the machine to its rearmost position ensuring the reverse percussive action manually by pulling at the air feeding hose. The reverse travel of the valving member from the rearmost to the frontmost position is done by the spring. The lock means of the valving member is engaged when compressed air is admitted, and disengaged when the supply of compressed air is terminated. Inherent in the aforedescribed machine is a major disadvantage in that it requires two attendants to control the operation of the machine, one of the attendants looking after the supply of compressed air, while the other pulling at the air feeding hose at the hole mouth.